Zr-89标记anti-CD11b导向的超声微泡用于评估腹主动脉瘤破裂风险的多模态分子影像研究

Inflammation plays a critical role in the rupture of abdominal aortic aneurysm (AAA). Up till now, there is still lack of effective method for assessing inflammatory status within the wall of AAA. We previously fabricated a nuclear probe, namely 99mTc-MAG3-anti-CD11b-Ab, based on which, we succeeded in detecting inflammatory atherosclerotic plaques by SPECT/CT imaging. From this result, we deem that CD11b is an important target for inflammatory cells. As AAA shares similar pathophysiological process of inflammation with atherosclerosis, we hypothesize that CD11b may be an important target for fabricating new PET imaging probe to detect inflammation within the wall of AAA. In order to verify this hypothesis, we herein attempt to conjugate nanoscale microbubble with anti-CD11b-Fab as targeting molecule and label it with Zr-89 to generate an ultrasound-PET imaging probe, taking advantage of the high resolution of ultrasound in imaging regional vessels. Based on this bi-modality imaging technique, we hope to detect inflammatory status within the wall of AAA and assessing its rupture risk. This study may provide a new method for looking insight into the status of inflammation within the wall of AAA and allows for assessing rupture risk of AAA by virtue of non-invasive molecular imaging method. Hopefully, this bio-modality imaging system may serve as a novel strategy for early detecting rupture-prone AAA and achieving its rupture-risk stratification, eventually facilitate to accurate selection of optimal AAA patients for surgeries.

管壁炎症是腹主动脉瘤（AAA）破裂的重要危险因素，目前缺乏评估AAA管壁炎症的有效手段。我们前期基于99mTc-MAG3-anti-CD11b-Ab SPECT/CT检测动脉粥样硬化易损斑块炎症状况的研究发现CD11b是炎症细胞的重要标志分子；考虑到AAA与动脉粥样硬化有相似的管壁炎症反应过程，提出“CD11b是研制新型AAA PET炎症显像剂的潜在重要靶标”的假说。为验证该假说，本项目尝试联合超声在血管显像方面具有局部分辨率高的优势，以纳米级微泡为载体，偶联anti-CD11b-Fab片段作为靶向分子，通过Zr-89进行标记，构建靶向炎症的超声与PET双模态显像剂，通过增强超声和PET/CT双模态显像评估AAA管壁炎症状况及破裂风险。本项目的完成有望通过无创分子影像深入了解AAA管壁炎症状况，为易损性AAA的检测和危险分层提供新的诊断思路和评估手段，促进AAA患者手术适应症的准确把握。

活跃的管壁炎症是预示主动脉瘤破裂的重要危险因素，然而目前缺乏有效的评估手段。预定位显像策略具有影像对比度好、对正常组织器官辐射损伤小、能够使用短半衰期放射性核素的优点。最好的预定位方法是基于1,2,4,5-四嗪（1,2,4,5-terazine，Tz）与反式环辛烯（Trans-cyslooctene，TCO）的反电子需求Diels-Alder环加成（inverse electron demand Diels-Alder cycloaddition, IEDDA）生物正交点击化学系统，其反应速率快、效率高、且无需催化剂，在肿瘤显像应用较多，但在动脉瘤显像未见报告。本研究合成预定位分子探针Anti-CD11b-TCO用于靶向不稳定动脉瘤管壁炎症，再通过99mTc-HYNIC-Tz与之体内点击，通过SPECT/CT实现小鼠富炎症主动脉瘤显像。合成的Anti-CD11b-TCO具有较高的TCO偶联率；99mTc-HYNIC-Tz放化学纯高（>95%）、体外稳定及血代谢动力学快；二者于体外点击转化率高（约89%）；反应产物99mTc-HYNIC-Tz/TCO-anti-CD11b对炎症细胞具有较高的亲和性和特异性。以胡索酸-3-氨基丙腈喂养C57BL/6J小鼠4周（1g/kg/day）构建不稳定主动脉瘤模型，注射anti-CD11b-TCO（100μg/只）预定位24小时，模型鼠注射同型IgG-TCO及非模型C57BL/6J小鼠注射anti-CD11b-TCO作为对照组；注射99mTc-HYNIC-Tz约2小时后行SPECT/CT显像，结果显示99mTc-HYNIC-Tz/TCO-anti-CD11b预定位显像能清晰显影小鼠富炎症主动脉瘤，且信噪比高（6.139±1.211），显著高于模型鼠99mTc-HYNIC-Tz/TCO-IgG显像（2.673±0.605, p<0.001）及非模型鼠99mTc-HYNIC-Tz/TCO-anti-CD11b显像（2.658±0.523, p<0.001）。离体动脉BSGI显像及病理免疫组化证实了活体SPECT/CT显像结果。总之，以anti-CD11b-TCO/Tz-HYNIC-99mTc预定位介导的SPECT/CT显像可检测主动脉瘤炎症，评估主动脉瘤的不稳定性，有望为临床主动脉瘤不稳定性提供有效的检测方法及抗炎疗效评价手段。